Sensor pixel circuitry for fingerprint identification

ABSTRACT

In one aspect, a fingerprint sensor device for fingerprint detection includes an array of sensor pixels to capacitively couple with a touched portion of a finger to form an array of fingerprint associated capacitors having capacitive values indicative of a fingerprint. Each sensor pixel includes: an output terminal configured to output an output signal that indicates a local capacitive coupling with the touched portion of the finger as part of fingerprint data for fingerprint detection; a capacitive sensing layer including an electrically conductive material that can be capacitively coupled to a local part of the touched portion of the finger, forming a fingerprint associated capacitor, the capacitive sensing layer operable to be coupled to the output terminal to cause the output signal; an integrated circuit layout layer that is electrically conductive; a fingerprint voltage generator; and a layout voltage generator.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.15/237,019, filed on Aug. 15, 2016, which is a continuation ofInternational Application No. PCT/CN2014/088522, filed on Oct. 13, 2014,both of which are hereby incorporated by reference in their entireties.

TECHNICAL FIELD

This patent document relates to sensor pixel circuitry and fingerprintidentification.

BACKGROUND

Various electronic devices or information systems can employ userauthentication mechanisms to protect personal data and preventunauthorized access. User authentication on an electronic device orinformation system can be carried out through one or multiple forms ofpersonal identification and authentication methods, including one ormore biometric identifiers. A biometric identifier can be used alone orin addition to a conventional authentication method, such as a passwordauthentication method. A popular form of biometric identifiers is aperson's fingerprint pattern. A fingerprint sensor can be built into theelectronic device to read a user's fingerprint pattern so that thedevice can only be unlocked by an authorized user of the device throughauthentication of the authorized user's fingerprint pattern. In someimplementations, such as fingerprint sensor can include sensor pixelcircuitry with pixelated pixel sensor elements for capturing fingerprintpatterns for user identification.

SUMMARY

In one aspect, a fingerprint sensor device for fingerprint detectionincludes an array of sensor pixels configured to capacitively couplewith a touched portion of a finger to form an array of fingerprintassociated capacitors having capacitive values indicative of afingerprint. Each sensor pixel includes an output terminal configured tooutput an output signal that indicates a local capacitive coupling withthe touched portion of the finger as part of fingerprint data forfingerprint detection. Each sensor pixel includes a capacitive sensinglayer including an electrically conductive material that can becapacitively coupled to a local part of the touched portion of thefinger, forming a fingerprint associated capacitor, the capacitivesensing layer operable to be coupled to the output terminal to cause theoutput signal. Each sensor pixel includes an integrated circuit layoutlayer that is electrically conductive and is capacitively coupled to aground terminal, forming a layout associated capacitor, the layout layeroperable to be coupled to the output terminal. Each sensor pixelincludes a fingerprint voltage generator electrically coupled to supplypower to the capacitive sensing layer to generate a fingerprint voltageto charge the fingerprint associated capacitor. Each sensor pixelincludes a layout voltage generator electrically coupled to supply powerto the integrated circuit layout layer to generate a layout voltage tocharge the layout associated capacitor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram showing an exemplary fingerprint sensordevice.

FIG. 1B is a diagram showing an exemplary sensor chip.

FIG. 2 is a schematic diagram of exemplary sensor pixel circuitry.

FIG. 3 is a schematic diagram of an equivalent circuitry of the sensorpixel circuitry in FIG. 1.

FIG. 4 is a schematic diagram of exemplary sensor pixel circuitry within-pixel integrator.

FIG. 5 is a schematic diagram of an equivalent circuitry of the sensorpixel circuitry in FIG. 4.

FIG. 6 is a schematic diagram of an exemplary sensor pixel circuitry.

FIG. 7 is a schematic diagram of an exemplary fingerprint identificationsystem.

FIG. 8 is a schematic diagram illustrating exemplary waveforms ofassociated signals.

FIG. 9 is a schematic diagram of exemplary sensor pixel circuitry and anexternal electrode according to an embodiment of the present document.

FIG. 10 is a schematic diagram illustrating waveforms of clock signalsaccording to an embodiment of the present document.

FIG. 11 is a schematic diagram illustrating yet another exemplary sensorpixel circuitry to compensate for capacitor mismatch in a fingerprintidentification system.

FIG. 12 is a schematic diagram illustrating yet another exemplary sensorpixel circuitry to compensate for capacitor mismatch in a fingerprintidentification system.

FIG. 13 is a schematic diagram illustrating yet another exemplary sensorpixel circuitry to compensate for capacitor mismatch in a fingerprintidentification system.

FIG. 14A is a schematic diagram illustrating an exemplary fingerprintidentification system for sharing integrators between sensor pixelcircuitry.

FIG. 14B is a schematic diagram illustrating another exemplaryfingerprint identification system for sharing integrators between sensorpixel circuitry.

FIG. 14C is a schematic diagram illustrating an exemplary fingerprintidentification system for sharing integrators between two sensor pixelcircuitry.

FIG. 14D is a schematic diagram illustrating an exemplary fingerprintidentification system for sharing integrators between two sensor pixelcircuitry.

DETAILED DESCRIPTION

Capacitive fingerprint identification devices and systems sensecapacitance variations to determine ridges and valleys of a user'sfinger. A low signal-to-noise ratio (SNR), when present in thecapacitive fingerprint identification system, lowers the accuracy offingerprint identification. One technique for increasing the SNR uses ametal ring to transmit an excitation signal directly to the finger to beidentified to enhance the identification accuracy. The metal ringoccupies valuable space on a semiconductor layout for the device, whichincreases product cost and affect appearances of products.

FIG. 1A is a block diagram showing an exemplary fingerprint sensordevice 1. The fingerprint sensor device 1 includes a sensor chip 2disposed over a substrate carrier 4 and a protective film or cover layer6 disposed over the sensor chip 2. The protective film or cover layer 6can include an insulator or dielectric material such as glass, silicondioxide (SiO₂), sapphire, plastic, polymer, other substantially similarmaterials. The protective film or cover layer 6 can be present toprotect the sensor chip 2 and potentially function as a part of adielectric layer between a surface of a finger 8 and conductive sensingelectrodes of individual sensor pixels in the sensor chip 2. Theprotective film or cover layer 6 is an optional layer depending on theapplication of the fingerprint sensor device 1. The fingerprint sensordevice 1 can be disposed through an opening of a top cover glass of anelectronic device such as a mobile phone or under a top cover glass ofthe electronic device. When used in the under-the-glass application, theprotective film or cover 6 is not needed because the top cover glass ofthe electronic device will function to protect the sensor chip 2 and actas the dielectric layer. The sensor chip 2 includes an array of sensorpixels that in combination senses or captures fingerprint data from thefinger 8 in contact with the protective film or cover layer 6. Eachsensor pixel of the sensor chip 2 generates an output signal (e.g., avoltage) based on a capacitance of a capacitor associated with a ridgeor valley of the finger 8. The output signals when combined represents afingerprint image of the finger 8. Higher the number of pixel sensors,greater the resolution of the fingerprint image.

FIG. 1B is a diagram showing an exemplary sensor chip 2. The sensor chip2 can include a pixelated sensor array 3 which can occupy a significantportion of the sensor chip 2. Each sensor pixel in the pixelated sensingelement array 3 can include a CMOS capacitive sensor or other types ofsensors that can sense fingerprint features. The sensor chip 2 caninclude a signal processing unit 5 for processing signals received fromall of the sensor pixels in the pixelated sensor array 3, and aconnection unit 7 electrically coupled to the signal processing unit 5.The signal processing unit 5 can include various signal processingcomponents including amplifiers, filters, and an analog to digitalconverter (ADC). The connection unit 7 can include multiple electrodeswhich can be connected to external circuitry through wire-bonding, bumpbonding or other connection means. The connection unit 7 can be disposedalong an edge of the sensor chip 2 for the convenience of interfacingwith other components of the fingerprint sensor device 1.

The array 3 of sensor pixels in the sensor chip 2 can be arranged tohave various shapes and sizes. For example, the array 3 of sensor pixelscan be arranged to have a rectangular shape with a width of therectangular shape being larger than a height of the rectangular shape.Exemplary sizes for the rectangular shaped sensor chip can include24×88, 32×88, 56×88 sensor pixels. In some implementations, the array 3of sensor pixels in the sensor chip 2 can be arranged to have a squareshape. Exemplary sizes for the square shaped sensor chip 2 include32×32, 64×64, 96×96 and 128×128 sensor pixels.

FIG. 2 is a schematic diagram of an exemplary sensor pixel circuitry 10according to an embodiment of the disclosed technology. The sensor pixelcircuitry 10 corresponds to at least part of the structure within eachsensor pixel in the array 3 of sensor pixels. The sensor pixel circuitry10 includes a capacitive sensing layer 100, a layout layer 106, voltagegenerators 102 and 104, and switching circuitry such as switchingnetworks 108 and 110. In some implementations, the circuitry ofswitching networks 108 and 110 can be implemented using sample-and-holdcircuitry. Within each sensor pixel, the capacitive sensing layer 100can be a conductive layer or electrode layer and can be implemented asone of the opposing sensor plates or electrodes in a capacitor. Whendisposed opposite to a surface of the finger, the capacitive sensinglayer 100 and the surface of the finger (e.g., a ridge or a valley ofthe finger) form the two opposing plates of a capacitor. The capacitivesensing layer 100 can include a metal layer within an integratedcircuitry (IC) layout, which forms a capacitor C1 with a groundterminal. Over the capacitive sensing layer 100, a passivation layer(not illustrated in FIG. 1) is usually disposed to cover the capacitivesensing layer 100, for receiving a touch of a user. The passivationlayer can be the protective film or cover layer 6 shown in FIG. 1A. Insome implementations, e.g., under the glass configuration, thepassivation layer is a top cover glass of an electronic device thatfunction to protect the sensor chip 2 and act as the dielectric layer.The passivation layer can include insulating materials such as a glass,a sapphire, a plastic or a polymer, etc.

When a finger of the user approaches the capacitive sensing layer 100, acapacitance value of the capacitor C1 varies accordingly. The layoutlayer 106 can be a poly layer of conductive (e.g., metal) layersutilized for IC layout. The layout layer 106 forms a capacitor Cp2 witha signal ground terminal. The signal ground terminal is not limited to asystem ground terminal with 0 voltage. A terminal or a layout layerreceiving a fixed voltage is considered as a signal ground terminal. Thecapacitor Cp2 can be a parasitic capacitor between the layout layer 106and another layout layer, or include a capacitor coupled between thelayout layer 106 and the signal ground terminal. The voltage generators102 and 104 can generate drive voltages V1 and V2. The switching network108 includes switches S1 and S2. The switches S1 and S2 are connected inseries, and the capacitive sensing layer 100 is electrically coupledbetween the switches S1 and S2. The switching network 110 includesswitches S3 and S4. The switches S3 and S4 are connected in series, andthe layout layer 106 is electrically coupled between the switches S3 andS4.

The switches S1 and S2 can be controlled by a clock signal or othercontrol signals, such that the switching network 108 turns on anelectrical connection between the voltage generator 102 and thecapacitive sensing layer 100 by switching on the switch S1 and turns offan electrical connection between the capacitive sensing layer 100 andthe output terminal N by switching off the switch S2 during a firstperiod. During a second period, the switching network 108 turns off theelectrical connection between the voltage generator 102 and thecapacitive sensing layer 100 by switching off the switch S1 and turns onthe electrical connection between the capacitive sensing layer 100 andthe output terminal N by switching on the switch S2. Thus, switch S1operates as a charging switch and switch S2 operates as a charge sensingswitch to synchronously charge and sense capacitor C1 associated withthe capacitive sensing layer 100 during respective time periods.

Similarly, the switches S3 and S4 can be controlled by a clock signal orother control signals, such that the switching network 110 turns on anelectrical connection between the voltage generator 104 and the layoutlayer 106 by switching on switch S3 and turns off an electricalconnection between the layout layer 106 and the output terminal N byswitching off switch S4 during the first period. During the secondperiod, the switching network 110 turns off the electrical connectionbetween the voltage generator 104 and the layout layer 106 by switchingoff switch S3 and turns on the electrical connection between the layoutlayer 106 and the output terminal N by switching on switch S4. Thus,switch S3 operates as a charging switch and switch S4 operates as acharge sensing switch to synchronously charge and sense capacitor Cp2associated with the integrated circuit layout layer 106 duringrespective time periods.

The switching networks 108 and 110 can adequately charge the capacitorsC1 and Cp2 using the voltage generators 102 and 104, and output thecharging result through the output terminal N to enhance an accuracy offingerprint identification. In addition, the voltage generators 102 and104 can vary the voltages generated V1 and V2 to enhance the accuracy offingerprint identification.

For example, the capacitor C1 formed between the capacitive sensinglayer 100 and the ground terminal can include a parasitic capacitor Cp1formed between the capacitive sensing layer 100 and the ground terminal,and a touch sensing capacitor Cf formed when the user's finger (e.g., aridge of the finger) is touching the passivation layer over thecapacitive sensing layer 100. The capacitor C1 represents an equivalentcapacitor between the capacitive sensing layer 100 and the groundterminal, which is a combination of the parasitic capacitor Cp1 and thetouch sensing capacitor Cf connected in parallel (i.e., C1=Cp1+Cf). Whenthe user's finger is not in contact with the passivation layer over thecapacitive sensing layer 100, the capacitance value of the touch sensingcapacitor Cf is substantially 0, and when the user's finger touches thepassivation layer over the capacitive sensing layer 100, the touchingcapacitor Cf has a nonzero capacitance value that depends on the spacingfrom the capacitive sensing layer 100. Therefore, the capacitance valueof the capacitor C1 varies according to whether the user's fingertouches the passivation layer over the capacitive sensing layer 100 andthe local spacing between a location on the touched part of the fingerand the layer 100. When the finger of the user touches the passivationlayer over the capacitive sensing layer 100, the capacitance value ofthe touch sensing capacitor Cf varies from one part of the finger toanother part according to a distance between the portion of the finger(e.g., a ridge of the finger) touching the passivation layer over thecapacitive sensing layer 100 and the capacitive sensing layer 100. Thisvariation in the touch sensing capacitor Cf is captured by the array ofsensor pixels and the output of the array of sensor pixels provides amap representing the surface profile of the touched portion of thefinger and thus can be used to reconstruct the fingerprint pattern. Thisreconstruction based on the spatial variation in the touch sensingcapacitor Cf can be achieved by the subsequent signal processingcircuitry. A fingerprint identification system that implementsstructures and functions substantially equivalent to the sensor chip 2in FIG. 1B includes a signal processing unit (e.g., substantiallysimilar to the signal processing unit 5 of the sensor chip 2) incommunication with the sensor pixel circuitry (e.g., substantiallysimilar to the array 3 of sensor pixels) can sense the capacitancevariation of the touch sensing capacitor Cf, and determine a location ofthe capacitive sensing layer 100 corresponds to a ridge or valley of thefinger touching the passivation layer over the capacitive sensing layer100.

FIG. 3 is a circuit diagram showing an exemplary circuit equivalent ofthe sensor pixel circuitry 10. The switches S1 through S4 are controlledby a clock signal to control the on-off states of the switches. Theswitches S2 and S4 are turned off when the switches S1 and S3 are turnedon, and the switches S2 and S4 are turned on when the switches S1 and S3are turned off. During the first period when switches S1 and S3 areturned on and switches S2 and S4 are turned off, voltage V1 chargescapacitor C1, and voltage V2 charges capacitor Cp2. During the secondperiod when switches S1 and S3 are turned off and switches S2 and S4 areturned on, the capacitor C1 exchanges electric charges with capacitorCp2 to form a resulting voltage Vr at the output terminal N. Moreover, avoltage value of the resulting voltage Vr can be represented using thefollowing equations:

${Vr} = {\frac{{V\; 1C\; 1} + {V\; 2{Cp}\; 2}}{{C\; 1} + {{Cp}\; 2}}.}$

Therefore, the sensor pixel circuitry 10 can output the resultingvoltage Vr to a signal processing unit of a fingerprint identificationsystem to determine whether the location of the sensor pixel circuitry10 corresponds to a ridge or a valley of the fingerprint according tothe resulting voltage Vr.

FIG. 4 is a schematic diagram of an exemplary sensor pixel circuitry 30according to an embodiment of the disclosed technology. FIG. 5 is aschematic diagram of an equivalent circuitry of the sensor pixelcircuitry 30. The sensor pixel circuitry 30 is substantially similar tothe sensor pixel circuitry 10. Different from the sensor pixel circuitry10, the sensor pixel circuitry 30 includes an integrator INTelectrically coupled to the output terminal N, for storing the electriccharges V1*Cf caused by ridges and valleys touching the passivationlayer over the capacitance sensing layer 100. The inclusion of theintegrator INT enhances the signal-to-noise ratio (SNR). The integratorINT includes a reference voltage generator 300, an amplifier OP, anintegrating capacitor Cint and a reset switch Srst. The referencevoltage generator 300 can generate a reference voltage Vref. Theamplifier OP includes a positive input terminal electrically coupled tothe reference voltage generator 300 for receiving the reference voltageVref, a negative input terminal electrically coupled to the outputterminal N for receiving the resulting voltage Vr, and an outputterminal for outputting an output voltage Vo. The integrating capacitorCint and the reset switch Srst are electrically coupled between thenegative input terminal of the amplifier OP and the output terminal.

A capacitance value of the parasitic capacitor Cp1 within the capacitorC1 is usually larger than a capacitance value of the touch sensingcapacitor Cf, which makes it difficult to identify a variation in thecapacitance of the touch sensing capacitor Cf. The voltage value of thereference voltage Vref received by the negative input terminal of theamplifier OP in the sensor pixel circuitry 30 can be adjusted, such thatthe capacitance variation of the touch sensing capacitor Cf is moreprominently identified through the integrator. In some implementations,the reference voltage Vref can be set as the resulting voltage Vr inabsence of a finger touch from the user (i.e., Cf=0), which isrepresented by

${Vref} = {\frac{{V\; 1{Cp}\; 1} + {V\; 2{Cp}\; 2}}{{{Cp}\; 1} + {{Cp}\; 2}}.}$

In absence of the finger touch, the total electric charges accumulatedby the capacitor C1 and the capacitor Cp2 during the first period arelarger than Vref*(Cp1+Cp2), and there are electric charges to be storedin the integrating capacitor Cint. When the electric charges stored inthe integrating capacitor Cint are mostly attributed to the touchsensing capacitor Cf, the output voltage Vo reflects the capacitancevalue of the touch sensing capacitor Cf more prominently. Adequatelydesigning the reference voltage Vref can reduce or even eliminate theeffect of the parasitic capacitor Cp1 on the determination of thecapacitance value of the touch sensing capacitor Cf.

In various circuitry designs, the capacitance values of the capacitorsCp1 and Cp2 may not be easily acquired. In some implementations, whenthe capacitance values of the capacitors Cp1, Cp2 are assumed to beequal, the reference voltage Vref can be set as

${Vref} = {\frac{1}{2}{\left( {{V\; 1} + {V\; 2}} \right).}}$

At least one of the voltages V1, V2, Vref can be generated by thevoltage generators 102 and 104. The reference voltage generator 300 canbe adjusted to provide V1*Cp1+V2*Cp2=Vref*(Cp1+Cp2), which can help toeliminate the capacitance mismatch of the capacitors Cp1 and Cp2 causedby the fabrication process. By changing the voltage V1 generated by thevoltage generator 102, the capacitance mismatch of the capacitors Cp1and Cp2 due to fabrication process can be substantially eliminated.

In various IC layouts, the capacitors Cp1 and Cp2 can be designed tohave substantially equal capacitance value, the reference voltage Vrefcan be set as

${{Vref} = {\frac{1}{2}\left( {{V\; 1} + {V\; 2}} \right)}},$

and the voltage values of the voltages V1 and V2 can be adjusted tosubstantially eliminate the capacitance mismatch of the capacitors Cp1and Cp2 due to fabrication.

As described above, by charging the capacitors C1 and Cp2 and outputtingthe charging result through the output terminal N, the sensor pixelcircuitry of the disclosed technology can enhance the accuracy offingerprint identification. Various modifications can be made to theabove described sensor pixel circuitry (e.g., array of sensor pixels 3)and fingerprint identification system (e.g., sensor chip 2 that includesan array of sensor pixels 3 and a signal processing system 5). Forexample, to substantially eliminate the mismatch of the capacitors Cp1and Cp2, at least one of the voltages V1, V2, and Vref generated by thevoltage generators 102, 104, and the reference voltage generator 300 canbe adjusted. To adjust at least one of the voltages, a digital to analogconverter (DAC) can be used to output a variable voltage. For example,in some implementations, the voltage generator 102 can include a DAC,which is controlled to output the voltage V1 with a variable voltagevalue. In some implementations, the voltage generator 104 can include aDAC, which is controlled to output the voltage V2 with a variablevoltage value. In some implementations, the reference voltage generator300 can include a DAC, which is controlled to output the referencevoltage Vref with a variable voltage value.

In addition to the DAC, a switch adjusting mechanism can be provided togenerate the controllable or variable voltages V1 and V2. FIG. 6 is aschematic diagram of an exemplary sensor pixel circuitry 60 according toan embodiment of the disclosed technology. In one implementation, thesensor pixel circuitry 60 can be substantially similar to the sensorpixel circuitry 30. The sensor pixel circuitry 60 utilizes electriccharge supplying modules 602 and 604 to function as the voltagegenerators 102 and 104 of the sensor pixel circuitry 30 in FIGS. 2, 3 4and 5. The electric charge supplying module 602 is electrically coupledbetween the switch S2 and the capacitive sensing layer 100. The electriccharge supplying module 604 is electrically coupled between the switchS4 and the layout layer 106. The electric charge supplying module 602includes the switches S11 and S12 electrically coupled to a voltage V+and a voltage V−, respectively. Similarly, the electric charge supplyingmodule 604 includes the switches S31 and S32 electrically coupled to avoltage V+ and a voltage V−, respectively. By controlling the on-offstates of the switches S11, S12, S31, and S32, the controllable orvariable voltages V1 and V2 can be generated to change the amount ofelectric charge stored in the capacitors C1 and Cp2, and substantiallyeliminate a capacitance mismatch of the capacitors Cp1 and Cp2 due tothe fabrication process.

FIGS. 7 through 8 illustrate exemplary embodiments of a fingerprintidentification system using an exemplary sensor pixel array arrangementto detect a presence of a ridge or valley of a finger at a specificlocation of the single sensor pixel circuitry. Proper arrangement of thesensor pixel circuitry in a fingerprint identification system can assistin identification of a user's fingerprint.

FIG. 7 is a schematic diagram of an exemplary fingerprint identificationsystem 70. The fingerprint identification system 70 is an implementationof the sensor chip 2 that combines the structures and functions of thearray 3 of sensor pixels in electrical communication with the signalprocessing system 5 as shown in FIG. 1B. The fingerprint identificationsystem includes an array of sensor pixel circuitry Pix_11 throughPix_MN, corresponding enable switches SW_11 through SW_MN, correspondinganalog to digital converters ADC_1 through ADC_M and a control module700. The sensor pixel circuitry Pix_11 through Pix_MN are arranged in anexemplary array configuration. For example, the array of sensor pixelcircuitry Pix_11 through Pix_MN are arranged in M rows and N columns.Each sensor pixel circuitry corresponds to and electrically coupled toan enable switch, and a row of sensor pixel circuitry correspond to andelectrically coupled to an analog to digital converter.

In one example configuration, the group (e.g., row or column) of sensorpixel circuitry Pix_11 through Pix_1N are electrically coupled to theanalog to a corresponding digital converter ADC_1. Similarly, the groupof sensor pixel circuitry Pix_21 through Pix_2N are electrically coupledto the analog to digital converter ADC_2. Remaining groups of sensorpixel circuitry can be similarly electrically coupled to correspondinganalog to digital converters.

The array of sensor pixel circuitry Pix_11 through Pix_MN and the enableswitches SW_11 through SW_MN are electrically coupled to the controlmodule 700 for receiving control signals generated by the control module700. Each sensor pixel circuitry of the array of sensor pixel circuitryPix_11 through Pix_MN can be substantially similar to the sensor pixelcircuitry 30 or 60 or any other configurations described in this patentdocument. Moreover, output voltages Vo_11 through Vo_MN are outputted bythe integrators of the sensor pixel circuitry Pix_11 through Pix_MN. Asdescribed below in this patent document, multiple sensor pixel circuitrycan share one integrator for various potential advantages including tosave layout space and to simplify the design, for example. Theoperational principles and detail operations of each sensor pixelcircuitry in the array of sensor pixel circuitry Pix_11 through Pix_MNcan be substantially similar to the description of the sensor pixelcircuitry 30 or 60 or any other configurations described in this patentdocument.

In the fingerprint identification system 70, the control module 700controls the enable switches SW_11 through SW_MN, such that a conductingperiod of an enable switch corresponding to a given sensor pixelcircuitry in the array of sensor pixel circuitry (e.g., Pix_11 throughPix_MN) and a conducting period of an enable switch corresponding toanother sensor pixel circuitry of the same row of sensor pixel circuitry(e.g., Pix_11 through Pix_MN) can differ in time. For example, thecontrol module 700 selectively turns on and off the switches SW_11through SW_MN to selectively vary the conducting period of the differentsensor pixel circuitry in the same row (e.g., Pix_11 through Pix_MN) forreadout by ADC. The control module 700 can control the sensor pixelcircuitry for the other rows in a similar manner. In someimplementations, the control module 700 can turn on the enable switchesof the array of sensor pixel circuitry substantially in parallel. Forexample, the control module 700 can enable SW11 through SWMN atsubstantially the same time, so that ADC 1-M can readout data inparallel. Also, the control module 700 can scan through one or morelines (e.g., rows, columns, or other groups) at a time to readout all ofthe pixel output voltage.

FIG. 8 illustrates examples of waveforms of various signals associatedwith a fingerprint identification system. Specifically, the examplewaves shown in FIG. 8 are associated with row M of the rows of sensorpixel circuitry in FIG. 7. An output of an integrator (e.g., integratorINT) is represented by the output voltage Vo_m1. The control signal ofthe enable switch SW_m1 pulls high at a time t1 for a time period, andthe output voltage Vo_m1 is delivered to the analog to digital converterADC_m through the enable switch SW_m1. At some time after t1, thecontrol signal of the reset switch Srst pulls high at a time tr1, suchthat the integrating capacitor Cint of the sensor pixel circuitry Pix_m1is return to zero, so as to be ready for performing another integrationfor a next time period. Also, at the same time as the integrator of thesensor pixel circuitry Pix_m1 performing integration, the integrator ofthe sensor pixel circuitry Pix_m2 also performs integrationsubstantially simultaneously. Similarly, the control signal of theenable switch SW_m2 pulls high at a time t2 for a time period, and theoutput voltage Vo_m2 is delivered to the analog to digital converterADC_m through the enable switch SW_m2. The time t2 is at some time aftert1. Also, each of the sensor pixel circuitry Pix_m3 through Pix_mN candeliver the output voltages to the corresponding analog to digitalconverter ADC_m at different after time t2. The different time instancesfor sensor pixel circuitry Pix_m1 through Pix_mN may be non-overlappingtime instances. The analog to digital converter ADC_m receives theoutput voltage of each sensor pixel circuitry in the row of the sensorpixel circuitry Pix_m1 through Pix_mN.

Each sensor pixel circuitry within the array of sensor pixel circuitryPix_11 through Pix_MN includes a dedicated integrator. As such, theintegration processes of the different sensor pixel circuitry in a givenrow of sensor pixel circuitry (e.g., Pix_m1 through Pix_mN) can beperformed in parallel by the multiple integrators. With a fixedintegration period for each integrator, the fingerprint identificationsystem 70 can shorten an overall integration period for the array ofsensor pixel circuitry. Due to the parallel integration of the sensorpixel circuitry of all sensor pixel circuitry in the entire array ofsensor pixel circuitry Pix_11 through Pix_MN, the overall integrationperiod for a row of sensor pixel circuitry can be fixed (e.g., at aperiod longer than individual sensor pixel circuitry integration period)to allow a longer integration period for each sensor pixel circuitry inthe rows of sensor pixel circuitry Pix_m1 through Pix_mn. Because theindividual integration processes can be performed in parallel for allpixel sensor circuitry, the overall integration period can be reducedeven when the individual integration period is increased. Increasing theindividual integration period, while reducing the overall integrationperiod, can allow the noise to be sufficiently averaged, and the SNR ofthe sensor pixel circuitry can be further enhanced. Because each pixelintegrator can act as a pixel level signal (voltage) storage, and thestored signal can be readout later by a scan readout process using theADCs and control module, for example.

In operations, responsive to a finger touch (e.g., on a passivationlayer over the fingerprint identification system), a selected subset orthe entire array of sensor pixel circuitry can be enabled to integratethe selected subset or the entire array of sensor pixel circuitry. Theintegrating capacitor connected to the negative feedback path of eachintegrator can be used as a local memory to store the charges associatedwith the corresponding sensor pixel. Readout of the sensor pixel datacan be performed per selected group or subset of the array of sensorpixel circuitry, such as each row, column, etc. Readout process is arelatively quick compared to the integration process, and thus, parallelintegration of the selected subset or the entire array of sensor pixelcircuitry while the finger is touching the fingerprint identificationsystem (e.g., the passivation layer over the sensor pixel circuitry) canbe advantageous by not wasting the sensor pixel circuitry under thefinger touch.

The implementations described above are for illustrative purpose andvarious modifications to one or more aspects of the sensor pixelcircuitry and fingerprint identification system are possible. Forexample, in some implementations, the fingerprint identification systemcan apply an excitation signal directly to a finger via an electrode(e.g., a metal ring) to increase a voltage difference between twoterminals of the touch sensing capacitor Cf, such that more electriccharges are accumulated in the touch sensing capacitor Cf during thefirst period. Alternatively, the fingerprint identification system canapply a high voltage to the finger during the second period, such thatmore electric charges are stored in the integrating capacitor Cint.

FIG. 9 is a schematic diagram of an exemplary sensor pixel circuitry 90and an external electrode Et. The sensor pixel circuitry 90 can besubstantially similar to the sensor pixel circuitry 30 or 60. Differentfrom the sensor pixel circuitry 30, the switches S1 and S3 arecontrolled by the clock signal ck1, and the switches S2 and S4 arecontrolled by the clock signal ck2. When the clock signal ck1 is high,the switches S1 and S3 are turned on. When the clock signal ck1 is low,the switches S1 and S3 are turned off. When the clock signal ck2 ishigh, the switches S2 and S4 are turned on. When the clock signal ck2 islow, the switches S2 and S4 are turned off. In addition, the externalelectrode Et can be electrically connected to the clock signal ck2, soas to pull high the voltage applied to the user's finger through theexternal electrode Et during the second period (i.e., the period whenthe switches S2 and S4 are turned on and the switches S1 and S3 areturned off). By applying the high voltage to the user's finger, moreelectric charges are stored in the integrating capacitor Cint throughthe touch sensing capacitor Cf during the second period, such that thefingerprint identification system can isolate and determine thecapacitance of the touch sensing capacitor Cf more accurately.

FIG. 10 is a schematic diagram illustrating exemplary waveforms of clocksignals ck1 and ck2. In the example shown in FIG. 10, the clock signalsck1 and ck2 are inverted and out of phase with each other. When ck1 isset high, ck2 is set low.

Other modifications are possible. For example, in the fingerprintidentification system 70, a row of sensor pixel circuitry (e.g., Pix_m1through Pix_mN) are couple to a corresponding analog to digitalconverter (e.g., ADC_m). In some implementations, the sensor pixelcircuitry units can be divided into different groups of sensor pixelcircuitry. All sensor pixel circuitry in a given group can beelectrically coupled to the same corresponding analog to digitalconverter. The groups of sensor pixel circuitry can be determined usingrows, columns, a predetermined number of sensor pixel circuitry, aparticular shape (e.g., a square) or other groupings that allow anenable switch corresponding to a sensor pixel circuitry in one group tohave a different conducting period than another enable switchcorresponding to a sensor pixel circuitry in a different group.

Additional examples of modifications to the sensor pixel circuitry areshown FIGS. 11, 12 and 13.

FIG. 11 is a diagram showing another exemplary sensor pixel circuitry1100 for compensating for capacitor mismatch in a fingerprintidentification system. The exemplary sensor pixel circuitry can includea sensor plate or a capacitive sensing layer 1102 that can operate orfunction as one of two opposing conductive plates of a fingerprintassociated capacitor. For example, when a finger 1108 of a userapproaches the sensor plate or capacitive sensing layer 1102, a surfaceof the finger 1108 and the sensor plate of capacitive sensing layer 1102can operate or function as the two opposing plates of capacitor Cf. Thecapacitance of the capacitor Cf can vary based at least partly on adistance between the surface of the finger (e.g., a ridge) and thesensor plate or capacitive sensing layer 1102. The sensor plate orcapacitive sensing layer 1102 can include a conductive material, such asone of various metals. A voltage generator 1132 is electricallyconnected to the sensor plate 1102, which is electrically connected to asystem ground through the surface of the finger 108. The voltagegenerator can generate drive voltage VDD for charging the fingerprintassociated capacitor Cf. A switching circuitry, such as a switchingnetwork 1120 includes switches 1122 and 1124 in series for beingswitchable in electrically connecting the sensor plate 1102 to thevoltage generator 1132 and an output terminal 1140. In someimplementations, the switching circuitry 1120 can be implemented usingsample-and-hold circuitry.

The switches 1122 and 1124 can be controlled by a clock signal or othercontrol signals, such that the switching circuitry 1120 can turn on anelectrical connection between the voltage generator 1132 and the sensorplate 1102 by turning on the switch 1122 and turn off an electricalconnection between the sensor plate 1102 and the output terminal 1140 byturning off the switch 1124 during a first period. During a secondperiod, the sample-and-hold circuitry 1120 can turn off the electricalconnection between the voltage generator 1132 and the sensor plate 1102by turning off the switch 1122 and turn on the electrical connectionbetween the sensor plate 1102 and the output terminal 1140 by turning onthe switch 1124. Thus, switch 1122 operates as a charging switch andswitch 1124 operates as a charge sensing switch to synchronously chargeand sense capacitor Cf associated with the sensor plate 1102 duringrespective time periods.

Two substantially identical conductive layers, electrodes or plates 1104and 1106 can be disposed below the sensor plate 1102. The conductiveplate 1104 and the sensor plate 1102 can form a corresponding capacitorCP1. The conductive plate 1106 and the sensor plate 1102 can form acorresponding capacitor CP2.

When the two conductive plates 1104 and 1106 are substantiallyidentical, the respective capacitors CP1 and CP2 can share asubstantially similar capacitance. A switching circuitry, such as aswitching network 1126 can include switches 1128 and 1130 to switchablebetween electrically connecting the conductive plate 1104 to a voltagegenerator 1134 and ground 1144. The other conductive plate 1106 iselectrically connected to ground and not electrically controlled by theswitching circuitry 1126. The voltage generator 1134 can include a DAC11136 and a voltage buffer 1138 to generate and provide a variablevoltage to the conductive plates 1104. In some implementations, theswitching circuitry 1126 can be implemented using sample-and-holdcircuitry.

The switches 1128 and 1130 can be controlled by a clock signal or othercontrol signals, such that the switching circuitry 1126 can turn on anelectrical connection between the voltage generator 1134 and theconductive plate 1104 by turning on the switch 1128 and turn off anelectrical connection between the conductive plate 1104 and the ground1144 by turning off the switch 1130 during a first period. During asecond period, the switching circuitry 1126 can turn off the electricalconnection between the voltage generator 1134 and the conductive plate1104 by turning off the switch 1128 and turn on the electricalconnection between the conductive plate 1104 and the ground 1144 byturning on the switch 1130. Thus, switch 1128 operates as a chargingswitch and switch 1130 operates as a grounding switch to synchronouslycharge and ground capacitor CP1 associated with the sensor plate 1102during respective time periods.

In some implementations, the output terminal 1140 can be optionallyelectrically connected to an integrator 1142 for storing the electriccharges caused by ridges and valleys of a finger touching thepassivation layer over the sensor plate 1102. The inclusion of theintegrator INT enhances the signal-to-noise ratio (SNR). The integratorincludes an amplifier 1118 having a negative input electricallyconnected to the output terminal 1140 connected to the switchingcircuitry 1120. The amplifier 1118 has a positive input electricallyconnected to a reference voltage generator 1112 for receiving thereference voltage Vref. The reference voltage generator 1112 can includea DAC2 1114 and a voltage buffer 1116 for generating and providing avariable reference voltage. The amplifier 1118 includes an outputterminal 114 for outputting an output voltage Vpo. An integratingcapacitor Cint 1146 and a reset switch rst 1148 are electrically coupledin parallel between the negative input terminal of the amplifier OP 1118and the output terminal 1144.

When the two conductive plates 1104 and 1106 are substantially similar,the DAC1 1136 output can be set to VDD. During the first period CK1, theswitches 1122 and 1128 are turned on and switches 1124 and 1130 areturned off. The charge in CP2 will be Cp2*VDD and the charge in CP1 willbe 0. During the second period CK2, switches 1122 and 1128 are turnedoff and switches 1124 and 1130 are turned on. During the second period,the charges in CP1 and CP2 will exchange. When a finger is not touchinga passivation layer over the sensor plate 1102, the charge in Cf issubstantially zero, and the voltage at the negative input of theamplifier OP 1118 will be VDD/2. Because the two conductive plates 1104and 1106 can be substantially the same due to the identical layout, theDAC1 might be not necessary or become optional. By removing the DAC1,the DAC1 noise will no longer exist in the pixel output, which furtherenhances the SNR.

Also, the mismatch between parasitic capacitors CP1 and CP2 can becompensated using techniques illustrated and described with respect toFIGS. 12 and 13. FIG. 12 is a diagram showing yet another exemplarysensor pixel circuitry 1200 for compensating for capacitor mismatch in afingerprint identification system. The sensor pixel circuitry 1200 issubstantially similar to the sensor pixel circuitry 1100 with somevariations. For example, the switching circuitry 1126 is electricallyconnected between the conductive plate 1104 and a voltage generator 1202that does not include a DAC. The output of the voltage generator 1202preset to VDD. In addition, a third voltage generator 1212 iselectrically connected to another switching circuitry 1204. The thirdvoltage generator 1212 can include a DAC 1214 DAC1 in series with avoltage buffer 1216.

The switching circuitry 1204 includes switches 1206 and 1208 in seriesfor being switchable in electrically connecting a capacitor 1210 Ccbetween the voltage generator 1212 and a common node 1218 connecting tothe sensor plate 1102 and the switching circuitry 1120 (which isswitchable in electrically connecting to the output terminal 1140 andthe voltage generator 1132). The other terminal of the capacitor 1210 Ccis electrically connected to ground. See relevant description of FIG. 11for the circuit components of the sensor pixel circuitry 1200 that aresimilar to the sensor pixel circuitry 1100.

In the sensor pixel circuitry 1200, the final voltage VPO at the outputterminal 1144 without a finger touching a passivation layer over thesensor electrode 1102 during the second period is(CP1*VDD+Cc*VDAC)/(Cc+Cp1+Cp2). When the two conductive plates 1104 and1106 are substantially similar, VDAC is set to VDD/2. When twoconductive plates 1104 and 1106 are not substantially similar, VDAC isadjusted.

FIG. 13 is a diagram showing yet another exemplary sensor pixelcircuitry 1300 for compensating for capacitor mismatch in a fingerprintidentification system. The sensor pixel circuitry 1300 is substantiallysimilar to the sensor pixel circuitry 1200 with some variations. Forexample, the switching circuitry 1204 includes switches 1206 and 1208electrically connected in series for selectively electrically connectingthe capacitor Cc 1210 to the voltage generator 1202 and a fourth voltagegenerator 1220. The voltage generator 1220 can be set to VDD. The otherterminal of the capacitor Cc 1210 is electrically connected to a commonnode 1218 connecting to the sensor plate 1102 and the sample-and-holdcircuitry 1120 (which is switchable in electrically connecting to theoutput terminal 1140 and the voltage generator 1132). See descriptionsof FIG. 12 for the corresponding descriptions of the circuit componentsof the sensor pixel circuitry 1300 that are similar to the sensor pixelcircuitry 1200.

In the sensor pixel circuitry 1300, the final voltage VPO at outputterminal 1144 without a finger touch during the second period Ck2 is(CP1*VDD+Cc*Vdac)/(Cc+Cp1+Cp2). When two conductive plates 1104 and 1106are not substantially similar, VDAC is adjusted.

In some implementations, an integrator can be shared between a number ofsensor pixel circuitry units to reduce the total number of integratorsin the fingerprint identification system, which can provide a numberpotential advantages including cost reduction, layout size reduction,and simplicity in design, for example. Multiple units of sensor pixelcircuitry can share an integrator by multiplexing the output signalsfrom a selected number of sensor pixel circuitry units into a sharedintegrator. For example, when grouping the array of sensor pixelcircuitry units into rows, with each row assigned to an ADC, each sensorpixel circuitry unit in a row can share an integrator with one or moresensor pixel circuitry units in one or more rows of sensor pixelcircuitry. When grouping the sensor pixel circuitry in the array ofsensor pixel circuitry into columns, each sensor pixel circuitry in agiven column can share an integrator with one or more sensor pixelcircuitry in one or more columns.

FIGS. 14A and 14B show examples of configurations for sharingintegrators between sensor pixel circuitry units.

FIG. 14A is a diagram showing an example of a fingerprint identificationsystem 1400 for integrator sharing between rows in an array of sensorpixel circuitry units. The fingerprint identification system 1400includes a control module 1402, which can be substantially similar tothe control module 700 in FIG. 7. An array of sensor pixel circuitrySensor Pixel 11 through Sensor Pixel MN are grouped into rows 1 throughM. Each row in the array includes N columns of sensor pixel circuitry.In the example shown in FIG. 14A, every two rows of sensor pixelcircuitry share integrators. However, more than two rows of sensor pixelcircuitry can share integrators. The control module 1402 can selectivelyenable/disable each sensor pixel circuitry in the array by turning onand off corresponding enable switches SW11 through SW MN. The switchsignal can be one or multiple digital logic signals. By controlling theappropriate sensor pixel circuitry through the enable switches, thecontrol module 1402 can integrate any number of sensor pixel circuitryin the array in parallel. In the example shown in FIG. 14A, the controlmodule enables the odd row of sensor pixel circuitry (e.g., Sensor Pixel11 through Sensor Pixel 1N) to integrate all sensor pixels in the row.The pixels in the odd row can perform integration in parallel, and afterthe integration is completed, control module can scan each pixels toreadout their data using the ADCs. Then the control module can switch onthe even row of sensor pixel circuitry (e.g., Sensor Pixel 21 throughSensor Pixel 2N), which can share the integrators used by the odd row ofsensor pixel circuitry (e.g., Sensor Pixel 11 through Sensor Pixel 1N)to perform integration in parallel. All of the odd and even rows can beprocessed in similar manner. In some implementations, all odd rows canbe processed at substantially the same time in parallel. Then all of theeven rows can be processed at substantially the same time in parallel.In some implementations, any number of odd and even rows can beprocessed together in parallel. In addition, the even rows can beprocessed first in some implementations. Thus, the order of the even andodd rows is not limiting.

FIG. 14B is a diagram showing an exemplary fingerprint identificationsystem 1410 for integrator sharing between columns in an array of sensorpixel circuitry. The fingerprint identification system 1410 includes acontrol module 1402, which can be substantially similar to the controlmodule 700 in FIG. 7. An array of sensor pixel circuitry Sensor Pixel 11through Sensor Pixel 4N are grouped into columns 1 through 4. While morethan 4 columns can be included in an array, only 4 columns are shown inFIG. 14B for illustrative purposes. Each column in the array includes Nrows of sensor pixel circuitry. In the example shown in FIG. 14B, everytwo columns of sensor pixel circuitry share integrators. However, morethan two columns of sensor pixel circuitry can share integrators. Thecontrol module 1402 can selectively enable/disable each sensor pixelcircuitry in the array by turning on and off corresponding enableswitches SW11 through SW 4N. By controlling the appropriate sensor pixelcircuitry through the enable switches, the control module 1402 canintegrate any number of sensor pixel circuitry in the array in parallel.In the example shown in FIG. 14B, the control module enables the oddcolumn of sensor pixel circuitry (e.g., Sensor Pixel 11 through SensorPixel 1N) to integrate all sensor pixels in the odd column. The sensorpixels in the odd column can perform integration in parallel, and afterthe integration completed, control module can scan each sensor pixel toreadout the data using the ADCs. Then the control module can switch onthe even column of sensor pixel circuitry (e.g., Sensor Pixel 21 throughSensor Pixel 2N), which can share the integrators used by the odd columnof sensor pixel circuitry (e.g., Sensor Pixel 11 through Sensor Pixel1N) to perform integration in parallel. All of the odd and even columnscan be processed in similar manner. In some implementations, all oddcolumns can be processed at substantially the same time in parallel.Then all of the even columns can be processed at substantially the sametime in parallel. In some implementations, any number of odd and evencolumns can be processed together in parallel. In addition, the evencolumns can be processed first in some implementations. Thus, the orderof the even and odd columns is not limiting. Moreover in both FIGS. 14Aand 14B, the array of sensor pixels can be grouped in a way differentthan rows or columns and the integrator sharing can be implemented invarious ways depending on the grouping of the array of sensor pixels.

FIG. 14C is a diagram showing an exemplary sensor pixel circuitry andfingerprint identification system 1420 with two sensor pixel circuitrysharing an integrator. The fingerprint identification system 1420 showsa simple example where two sensor pixel circuitry 1422 and 1424 shareone integrator 1426. The sensor pixel circuitry 1422 and 1424 can besubstantially similar to sensor pixel circuitry 10 in FIG. 2 or anyother configurations described in this patent document.

FIG. 14D is a diagram showing an exemplary sensor pixel circuitry andfingerprint identification system 1430 with two sensor pixel circuitrysharing an integrator. The fingerprint identification system 1430 showsa simple example where two sensor pixel circuitry 1432 and 1434 shareone integrator 1436. The sensor pixel circuitry 1422 and 1424 can besubstantially similar to sensor pixel circuitry in FIGS. 11, 12 and 13or any other configurations described in this patent document.

In the examples shown in FIGS. 14A, 14B, 14C and 14D, some of thecomponents including the ADC are not included in the figures forillustrative purposes only.

Various implementations and examples of the disclosed technology havebeen described. The disclosed technology utilizes integrators forstoring the electric charges accumulated by the touch sensing capacitor,utilizes the voltage generator for outputting the variable voltage andadjusting the electric charges stored in the parasitic capacitors, andutilizes the sensor pixel circuitry with a dedicated integrator forperforming integration across a group of sensor pixel circuitry inparallel to enhance the SNR. The sensor pixel circuitry and thefingerprint identification system described in this patent documentprovide accurate fingerprint identification even without a metal ring.

While this patent document contains many specifics, these should not beconstrued as limitations on the scope of any invention or of what may beclaimed, but rather as descriptions of features that may be specific toparticular embodiments of particular inventions. Certain features thatare described in this patent document in the context of separateembodiments can also be implemented in combination in a singleembodiment. Conversely, various features that are described in thecontext of a single embodiment can also be implemented in multipleembodiments separately or in any suitable subcombination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. Moreover, the separation of various system components in theembodiments described in this patent document should not be understoodas requiring such separation in all embodiments.

Only a few implementations and examples are described and otherimplementations, enhancements and variations can be made based on whatis described and illustrated in this patent document.

What is claimed is:
 1. A fingerprint sensor device for fingerprintdetection, comprising: an array of sensor pixels configured tocapacitively couple with a touched portion of a finger to form an arrayof fingerprint associated capacitors having capacitive values indicativeof a fingerprint, each sensor pixel including: an output terminalconfigured to output an output signal that indicates a capacitivecoupling with the touched portion of the finger as part of fingerprintdata for fingerprint detection; a sensor plate capacitively coupled to apart of the touched portion of the finger, forming a fingerprintassociated capacitor; a first switching circuitry for being switchablein electrically connecting the sensor plate to a fingerprint drivingvoltage and the output terminal; a pair of layout electrodes, comprisinga first layout electrode capacitively coupled to the sensor plate forforming a first layout associated capacitor, and a second layoutelectrode capacitively coupled to the sensor plate for forming a secondlayout associated capacitor; a second switching circuitry for beingswitchable in electrically connecting the first layout electrode to alayout driving voltage and a ground terminal.
 2. The fingerprint sensordevice of claim 1, wherein the first switching circuitry comprises afingerprint charging switch and a charge sensing switch; the fingerprintcharging switch is electrically coupled between the fingerprint drivingvoltage and the sensor plate; the charge sensing switch is electricallycoupled between the sensor plate and the output terminal.
 3. Thefingerprint sensor device of claim 2, wherein the first switchingcircuitry is configured to turn on the fingerprint charging switch andturn off the charge sensing switch during a first period for enablingthe fingerprint driving voltage to charge the fingerprint associatedcapacitor, and to turn on the charge sensing switch and turn off thefingerprint charging switch during a second period for outputtingcharges of the sensor plate to the output terminal.
 4. The fingerprintsensor device of claim 1, wherein the first layout electrode and thesecond layout electrode are substantially identical conductive plates,and a capacitance of the first layout associated capacitor issubstantially similar to that of the second layout associated capacitor.5. The fingerprint sensor device of claim 1, wherein the second layoutassociated capacitor is electrically coupled to the ground terminal. 6.The fingerprint sensor device of claim 5, wherein the second switchingcircuitry comprises a layout charging switch and a grounding switch; thelayout charging switch is electrically coupled between the layoutdriving voltage and the first layout electrode; the grounding switch iselectrically coupled between the first layout electrode and the groundterminal.
 7. The fingerprint sensor device of claim 6, wherein thesecond switching circuitry is configured to turn on the layout chargingswitch and turn off the grounding switch during a first period forenabling the layout driving voltage to charge the first layoutassociated capacitor, and to turn on the grounding switch and turn offthe layout charging switch during a second period for exchanging chargesbetween the first layout associated capacitor and the second layoutassociated capacitor.
 8. The fingerprint sensor device of claim 1,wherein the first switching circuitry comprises a first switch and asecond switch electrically coupled in series between the fingerprintdriving voltage and the output terminal, and the sensor plate iselectrically coupled to a common node between the first switch and thesecond switch; the second switching circuitry comprises a third switchand a fourth switch; the first layout electrode is electrically coupledto the layout driving voltage via the third switch, and electricallycoupled to the ground terminal via the fourth switch.
 9. The fingerprintsensor device of claim 8, wherein the first switch and the third switchare turned on while the second switch and the fourth switch are turnedoff during a first period; the first switch and the third switch areturned off while the second switch and the fourth switch are turned onduring a second period.
 10. The fingerprint sensor device of claim 9,wherein the sensor pixel further comprises an integrator comprising: anamplifier having a negative input electrically coupled to the outputterminal, a positive input electrically coupled to a variable referencevoltage, and an output for outputting an output voltage; an integratorcapacitor electrically coupled between the negative input and the outputof the amplifier; and a reset switch electrically coupled in parallelwith the integrator capacitor.
 11. The fingerprint sensor device ofclaim 1, wherein the sensor pixel further comprises a compensatingcircuitry electrically coupled to the sensor plate for compensatingcapacitor mismatch between the first layout associated capacitor and thesecond layout associated capacitor.
 12. The fingerprint sensor device ofclaim 11, wherein the compensating circuitry comprises a third switchingcircuitry and a compensating capacitor, the third switching circuitry isswitchable in electrically connecting the compensating capacitor to acompensating voltage and the sensor plate.
 13. The fingerprint sensordevice of claim 12, wherein the third switching circuitry comprises afirst mismatch compensating switch and a second mismatch compensatingswitch; one terminal of the compensating capacitor is electricallycoupled to the compensating voltage via the first mismatch compensatingswitch, and electrically coupled to the sensor plate via the secondmismatch compensating switch; the other terminal of the compensatingcapacitor is electrically coupled to the ground terminal.
 14. Thefingerprint sensor device of claim 13, wherein the third switchingcircuitry is configured to turn on the first mismatch compensatingswitch and turn off the second mismatch compensating switch during afirst period; turn on the second mismatch compensating switch and turnoff the first mismatch compensating switch during a second period. 15.The fingerprint sensor device of claim 11, wherein the compensatingcircuitry comprises a third switching circuitry, and a compensatingcapacitor electrically coupled between the sensor plate and the thirdswitching circuitry.
 16. The fingerprint sensor device of claim 15,wherein the third switching circuitry is switchable in electricallyconnecting the compensating capacitor to a first compensating voltageand a second compensating voltage.
 17. The fingerprint sensor device ofclaim 16, wherein the third switching circuitry comprises a firstmismatch compensating switch and a second mismatch compensating switch;one terminal of the compensating capacitor is electrically coupled tothe first compensating voltage via the first mismatch compensatingswitch, and electrically coupled to the second compensating voltage viathe second mismatch compensating switch; the other terminal of thecompensating capacitor is electrically coupled to the sensor plate. 18.The fingerprint sensor device of claim 17, wherein the firstcompensating voltage is set to be substantially same as the fingerprintdriving voltage and the layout driving voltage; the second compensatingvoltage is provided by a voltage generator comprising adigital-to-analog convertor and a voltage buffer connected in series.19. The fingerprint sensor device of claim 18, wherein the secondcompensating voltage is a variable voltage which is adjusted accordingto mismatch between the first layout electrode and the second layoutelectrode.
 20. The fingerprint sensor device of claim 17, wherein thecompensating capacitor is a metal-insulator-metal (MIM) capacitor or apoly-insulator-poly (PIP) capacitor in the sensor pixel.